PAF is a chemical substance released from human and other animal cells and is an acetylglyceryl ether of phosphorylcholine as represented by the following formula ##STR2## wherein .gamma. is the integer 15 or 17.
PAF is physiologically active and causes contraction of the airway smooth muscle, increased vascular permeation, platelet aggregation and blood pressure fall, among others. It is thought to be a factor inducing asthma, inflammation, thrombosis, shock and other symptoms. Therefore, studies of substances capable of antagonizing the physiological activities of PAF are under way and several anti-PAF agents have been reported (e.g. European Patent Application No. 178,261 (A), U.S. Pat. Nos. 4,539,332; 4,656,190 and 4,621,038 European Pat. No. 115,979 (B), and British Patent Application No. 2,162,062 (A)).
The present inventors found that novel saturated heterocyclic carboxamide derivatives differing in chemical structure from the known anti-PAF agents having platelet activating factor antagonizing activity and, based on this finding, they have now completed the present invention.